Planographic printing plates



United States Patent 3,256,810 PLANOGRAPHIC PRINTING PLATES Anthony L. Ensink, 2129 W. Morse Ave., Chicago 45, Ill. No Drawing. Filed Mar. 9, 1964, Ser. No. 350,555 8 Ciaims. (Cl. 101-1492) My present invention relates to certain innovations and improvements in paper base, planographic printing plates which have at least one planographic printing surface containing insolubilized alginate as a primary effective hydrophillic colloid. More specifically, my present invention relates to innovations and improvements in barrier or seal coatings or layers for planographic printing plates of the type mentioned.

In my prior Patent No. 2,806,424 I disclosed improved planographic printing plates having planographic printing surfaces containing insolubilized alginate as the sole effective hydrophillic colloid and an inert filler in finely divided form dispersed with the colloid. In my prior patent I disclosed a method of making planographic printing plates of the type described therein which method included the application of a water-proofing coating to a paper base or sheet prior to the deposition of the subsequent functional coatings which provided the planographic printing surface. Among the coatings that were mentioned as providing a suitable waterproofing coating were those formed of casein, urea formaldehyde, melamine formaldehyde, cellulose derivatives, chlorinated rubber and varnishes.

In my Patent No. 2,835,576 I disclosed pre-sensitized planographic printing plates wherein the planographic printing surface contained insoluble polyvalent metal alginate as the adhesive colloid, a finely divided inert filler together, with a light sensitizing metal salt reactive to further harden the alginate upon exposure to light. In the manufacture of these pre-sensitized planographic printing plates waterproofing coatings were used for treating the paper base material or web of the same type as disclosed in my Patent No. 2,806,424.

While it is possible to use the disclosures of my aforeside patents to manufacture direct image masters or preprinted therefrom would have ink deposited where there should have been no ink deposited. After considerable investigation it was found that in making erasures on plates manufactured in accordance with my prior patents, if the printing surface coats were penetrated because of extensive erasing action, then the waterproofing layer or.

coating would be laid opened or exposed and that this would be hydrophobic. Of course, it is well understood that the printing surface of a planographic printing plate should be hydrophillic (i.e., water-receptive and greaseresistant) in all areas except where a grease-receptive image has been purposely deposited so as to pick up ink.

It is not to be understood from the foregoing that plates made in accordance with my prior patents were not satis factory since it is readily possible to make erasures on such plates without exposing underlying hydrophobic areas provided proper techniques are used in making such erasures. Furthermore, in certain instances it is actually beneficial to have paper planographic plates which do not lend themselves to unskilled erasures, such as for example plates used in check printing where erasures are undesired.

3,256,810 Patented June 21, 1966 I have discovered in accordance with the present inven tion that by first treating the paper raw stock or paper base web with a suitable preparatory coating it is possible to lay down thereon a seal or barrier coat which provides adequate moisture resistance for the plate but which will be hydrophillic so that no difficulty is experienced when erasures are made, even when made too vigorously or improperly. In other words, with my new seal or barrier coats, even if the hydrophillic seal or barrier is exposed as a result of erasures or other abrading action, ink will not be picked up in the abraded areas since they are hydrophillic.

In addition I have found that the improved seal or barrier coats of the present invention also provide a better degree of adhesion with the overcoats that provide the planographic printing surface. Evidently, the improved adhesion at the interface between the seal or barrier coat and the face or functional printing coat arises from the fact that alginate is present in both the seal and barrier coat as well as in the face or overcoat which provides the planographic printing surface. However, it is not necessary that alginate constitute the sole hydrophillic colloid in the planographic printing surface or coat although it is present as a primary effective hydrophillic colloid therein.

In view of the foregoing it will be seen that the object of the present invention, generally stated, is the provision of improved planographic printing plates formed on a paper base which will have a hydrophillic seal or barrier coating containing insolubilized alginate and which will carry thereover a planographic printing surface also containing insolubilized alginate as an effective primary colloid constituent.

An important object of the invention is the provision of improved planographic printing plates of the type mentioned which are readily manufactured on a quantity production basis using commercial coating and drying equipment, with the manufacturing steps involved being readily carried out so as to produce a quality product of high uniformity.

Certain other objects of the invention will, in part, be obvious and will in part appear hereinafter.

For a more complete understanding of the nature and scope of the invention reference may now be had to the following detailed description thereof wherein several examples are set forth illustrating the presently preferred embodiments of the invention.

Example I The paper base sheet or web used in carrying out this example may be any of the suitable known types or grades of raw stock heretofore used for making planographic printing plates.

Step 0ne.A paper web having a basis weight of approximately 60 pounds, based on a ream of 500 sheets cut to a size of 25 x 38 inches, is first coated on one side with about 8 to 10 pounds dry weight per ream of a seal or barrier coating composition having the following formulation, the coating being applied and dried in known manner on standard equipment:

' Lbs. 5% sodium alginate solution 60% kaolin clay slurry 16 30% colloidal silica dispersion 30 Dimethylol urea 2 The foregoing coating composition for the seal or barrier coat may be formulated from the specified ingredients in accordance with the following procedure:

The alginate solution is first prepared by dissolving suificient sodium alginate of commercial grade in water to give a 5% solution. The dispersion or slurry of the Kaolin clay in water (60% solids) is then prepared and b added to the alginate solution with stirring. This addition is followed by addition of the dispersion of the colloidal silica in water (30% solids), also with agitation. After these three ingredients have been thoroughly blended the dimethylol urea (DMU) is added to the batch and stirring is continued for 30-45 minutes. This coating formulation bath may be stored in a supply tank with mild agitation or stirring until required for use. The temperature of the batch is not critical and may range from 75 to 110 F. When the foregoing formulation is applied to the paper raw stock in the amounts above indicated the dimethylol urea will act to insolubilize the alginate, this insolubilization occurring during the drying operation.

The resulting coating laid down by the foregoing formulation is a seal or barrier coat Which is hydrophilic but which provides considerable and adequate moisture resistance to the paper base.

Step tw0.To the previously uncoated non-printing side (i.e., back side) of the paper web there is next applied in known manner a suitable back coating at the rate of about 10 pounds dry Weight per ream, having the following composition:

Lbs.

Water 26.4

Kaolin clay 100.0 Sodium tripolyphosphate (Calgon T, solution) 3.0

Casein, NH OH cut, 16.7% 49.5 Latex SB type, 48% solids (aqueous dispersion of discrete polymer particles of 60 parts styrene to 40 parts butadiene) 14.1

Step three.In this step the surface of the paper web that has already had the seal and barrier coat applied and dried thereon in step one is coated with a water base dispersion in which the main ingredients are sodium alginate and inert mineral pigment, a suitable formulation being as follows:

Parts Water 136.5 Sodium tripolyphosphate 0.3 Sodium alginate (Kelgin XL) 6.5 50% kaolin clay slip 54.0 Ammonia, 26 Br .7

If necessary a small amount of a suitable defoarner (e.g., tributyl phosphate or butanol) as well as a wetting agent solution may be incorporated. The above formulation is applied over the barrier or sealer coat at the rate of 8 to 10 pounds dry weight per ream.

Step f0ur.After the paper face coat has been applied as described in step three, a Wash coat is applied thereover which is essentially a water solution of polyvalent salts. The preferred formulation for the wash coat is one that contains parts of zinc acetate and 15 parts of aluminum chloride in 170 parts of Water. This coating is applied and dried in the usual manner. The polyvalent salts act upon the alginate content of the face or printing coat laid down in step three and serve to insolubilize the same.

In practicing Example I a number of variations may be introduced without basically departing therefrom. Among the changes or variations that may be made are the following:

1) In the sealor barrier coat the two parts of dimethylol urea may be replaced with from 0.45 to 2.0 parts melamine formaldehyde. This material is available commercially, two sources being under the proprietary names Parez Resin from American Cyanamid Company or Resloom M75 from Monsanto Chemical Company. Instead of using dimethylol urea or melamine formaldehyde, a special mixture comprising 63% by weight ethyl acrylate, 35% acrylonitrile and about 2% methacrylic acid may be used. Such a mixture is available commercially in the form of an emulsion containing 43-45% 4 solids from American Cyanamid Company under the proprietary name Cypel Resin Emulsion 205. Still other catalysts or cross-linking agents that can be used include urea formaldehyde and glyoxal.

(2) The kaolin clay in the barrier or seal coat formulation may be any one of several fine clays available to the paper making industry which are also referred to as china clay. The clay may be-replaced in whole or part by one or more inert pigment materials such as blanc fixe (barium sulfate), zinc oxide, titanium dioxide, and hydrated alumina.

(3) In the seal or barrier coating formulation the colloidal silica should contain silica with particle sizes ranging between 7 to 30 millimicrons. Preferably the particle size ranges from 7 to 17 millimicrons. Colloidal silicas with such a particle size distribution are marketed commercially by E. I. du Pont de Nemours under the tradenames Ludox S.M., Ludox LS, and Ludox HS. Also they are available from Monsanto Chemical Company under the tradename Syton 200. Methods of manufacturing such colloidal silicas are described in detail in Patents Nos. 2,244,325, 2,574,902 and 2,597,872. These colloidal silicas are generally marketed as 30% Si0 dispersions.

(4) It, will be appreciated that various back coating formulations may be used for preventing curl, stiffening the sheet, and imparting dimensional stability.

(5) The coating applied in step three to provide the planographic printing surface, and referred to as the face coat, may be varied as to formulation provided that it contains a substantial content or proportion of alginate as the hydrophillic adhesive component. Other colloids Which may be used to replace a portion of the alginatev are carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and casein.

(6) Other polyvalent salts may be used in the insolubilization or Wash coat to replace all or part of the aluminum chloride and zinc acetate. For example, other salts that may be used (alone or in combination) include Aluminum sulfate Aluminum acetate Aluminum formate Copper sulfate Copper chloride Cadmium chloride Ferric chloride Zinc chloride Zinc formate Zinc borate Zirconium acetate (7) If desired the wash coat containing the polyvalent salts may be dispensed with and the salts may be incorporated in and as part of the face coat, thereby eliminating one of the four coating operations. However, a certain. amount of ammonia hydroxide is required to dissolve the precipitate formed when bivalent and/ or multivalent salts are added directly to the adhesive. The ammonia hydroxide will be driven off during the drying operation, which then will serve to insolubilize the alginate.

(8) Instead of having a back coating for imparting dimensional stability and preventing curl the web may be given a seal or barrier coat on both faces and then provided with subsequent face coatings for providing the planographic printing surfaces.

(9) If desired pre-sensitized planographic printing plates may be made by incorporating in the face coating a salt such as ammonium bichromate or diazo salt such as Diazolith #1 from Edwal Laboratories, which will on drying leave a light sensitive form of insoluble polyvalent metal alginate. The disclosure contained in my Patent No. 2,835,576 may be followed in connection with preparing pre-sensitized plates using paper base stock that has received the improved seal or barrier coat provided by the present invention.

() Step one and step two may be reversed.

Certain other changes of a minor nature will be apparent to those skilled in-the art.

I claim:

1. A planographic printing plate comprising a paper base at least one side of which has dried thereon a hydrophillic seal and barrier coating applied as an aqueous dispersion which leaves a solids residue of from about 8 to 10 pounds per ream of 3300 square feet and consisting essentially of from about to of alginate, from about 35 to 40% of colloidal silica, from about 35 to 40% of inert mineral pigment, and up to about 12% of an alginate insolubilizing material, said alginate being in insolubilized condition and at least a portion of said insolubilizing material being reacted with said alginate, and said plate having dried over said seal and barrier coating an additional coating of from about 8 to 10 pounds dry basis per ream providing the planographic printing surface and comprising insolubilized alginate as a primary effective hydrophillic colloid intimately mixed with inert filler in finely divided form.

2. A planographic printing plate comprising a paper base at least one side of which has dried thereon a hydrophillic seal and barrier coating applied as an aqueous dispersion which leaves a solids residue of from about 8 to 10 pounds per ream of 3300 square feet and consisting essentially of approximately 1 part of alginate, approximately 2 parts of colloidal silica, approximately 2 parts of inert mineral pigment, and a fraction of one part of an alginate insolubilizer, said alginate being in insolubilized condition and at least a portion of said insolubilizing material being reacted with said alginate, and said plate having dried over said seal and barrier coating an additional coating of from about 8 to 10 pounds dry basis per ream providing the planographic printing surface and containing insolubilized alginate as a primary effective hydrophillic colloid.

3. The planographic printing plate of claim 2 wherein the alginate insolubilizer is approximately 0.4 part of dirnethylol urea.

4. The planographic printing plate of claim 2 wherein the alginate insolubilizer is melamine formaldehyde.

5. The planographic printing plate of claim 2 wherein the alginate insolubilizer is a mixture containing approximately 63% ethyl acrylate, about acrylonitrile and about 2% methacrylic acid.

6. The planographic printing plate of claim 2 wherein the inert mineral pigment consists of at least one pigment selected from the group consisting of kaolin clay, zinc oxide, hydrated alumina, titanium dioxide and barium sulfate.

7. The planographic printing plate of claim 2 wherein said paper base has a back coating on one side to prevent curl and impart dimensional stability.

8. The planographic printing plate of claim 2 wherein said additional dried coating providing the planographic printing surface is treated with a solution of at least one polyvalent salt selected from the group consisting of zinc acetate, zinc chloride, zinc formate, zinc borate, aluminum chloride, aluminum sulfate, aluminum acetate, aluminum formate, copper sulfate, copper chloride, cadmium chloride, ferric chloride, and zirconium acetate.

References Cited by the Examiner UNITED STATES PATENTS 2,534,650 12/1950 Worthen 10l.149.2 2,760,431 8/1956 Beatty 101-149.2 2,766,688 10/1956 Halpern et al 101-149.2 2,983,220 5/1961 Dalton et al. 101-l49.2 2,994,676 8/1961 Kuscan 117-155 3,055,295 9/1962 Perkins 101-149.2

DAVID KLEIN, Primary Examiner.

J. A. BELL, Assistant Examiner. 

1. A PLANOGRAPHIC PRINTING PLATE COMPRISING A PAPER BASE OF AT LEAST ONE SIDE OF WHICH HAS DRIED THEREON A HYDROPHILLIC SEAL AND BARRIER COATIG APPLIED AS AN AQUEOUS DISPERSION WHICH LEAVES A SOLIDS RESIDUE OF FROM ABOUT 8 TO 10 POUNDS PER REAM OF 3300 SQUARE FEET AND CONSISTING ESSENTIALLY OF FROM ABOUT 15 TO 20% OF ALGINATE, FROM ABOUT 35 TO 40% OF COLLOIDAL SILICA FROM ABOUT 35 TO 40% OF INERT MINERAL PIGMENT, AND UP TO ABOUT 12% OF AN ALGINATE INSOLUBILIZING MATERIAL, SAID ALGINATE BEING IN INSOLUBILIZED CONDITION AND AT LEAST A PORTION OF SAID INSOLUBILIZING MATERIAL BEING REACTED WITH SAID ALGINATE, AND SAID PLATE HAVING DRIED OVER SAID SEAL AND BARRIER COATING AN ADDITIONAL COATING OF FROM ABOUT 8 TO 10 POUNDS DRY BASIS PER REAM PROVIDING THE PLANOGRAPHIC PRINTING SURFACE AND COMPRISING INSOLUBILIZEDALGINATE AS A PRIMARY EFFECTIVE HYDROPHILLIC COLLOID INTEIMATELY MIXED WITH INERT FILLER IN FINELY DIVIDED FORM. 